U.S. patent number 3,585,368 [Application Number 04/848,550] was granted by the patent office on 1971-06-15 for apparatus for capacitively sensing information apertures in data cards.
Invention is credited to Thomas A. Nunamaker.
United States Patent |
3,585,368 |
Nunamaker |
June 15, 1971 |
**Please see images for:
( Certificate of Correction ) ** |
APPARATUS FOR CAPACITIVELY SENSING INFORMATION APERTURES IN DATA
CARDS
Abstract
Card reading apparatus comprising a plurality of input
conductors for disposition along one side of a data card
incorporating an electric shield and a plurality of readout
conductors for disposition along the opposite side of the card to
establish a capacitive coupling between the readout conductors and
the input conductors through selectively positioned apertures in
the shield representing recorded information. A plurality of
voltage stabilizing capacitors have output sides connected to the
respective readout conductors. A plurality of voltage stabilizing
amplifiers have inputs connected to the respective readout
conductors and outputs connected to the input sides of the
respective capacitors. Information receiving means is coupled to
the input side of each capacitor to respond to the change in
voltage applied thereto by the corresponding amplifier upon
energization of an input conductor to which the corresponding
readout conductor is coupled capacitively through an aperture in
the electric shield. The capacitance of each capacitor and the gain
of each amplifier operate together in response to an incipient
change in voltage on the corresponding readout conductor to restore
continuously the original voltage on the conductor so that the
input to the information receiving means is not rendered inaccurate
by spurious and parasitic capacitive relationships of the readout
conductors to adjacent structure.
Inventors: |
Nunamaker; Thomas A. (Oak Park,
IL) |
Family
ID: |
25303602 |
Appl.
No.: |
04/848,550 |
Filed: |
August 8, 1969 |
Current U.S.
Class: |
235/451; 235/488;
365/102 |
Current CPC
Class: |
G06K
7/081 (20130101) |
Current International
Class: |
G06K
7/08 (20060101); G06k 007/08 (); G11b 009/06 () |
Field of
Search: |
;235/61.11,61.11H
;340/173 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Cook; Daryl W.
Claims
I claim:
1. Apparatus for reading data cards incorporating an electric
shield apertured selectively in a pattern representing recorded
information, said apparatus comprising, in combination, a plurality
of input conductors disposed generally in mutually parallel spaced
relation to each other for disposition along one side of a card to
be read, means for applying a voltage to the individual input
conductors selectively, a plurality of readout conductors disposed
generally in mutually parallel spaced relation to each other for
disposition along the opposite side of the card to be read, said
readout conductors being oriented in a generally transverse cross
relation to said input conductors and being disposed in spaced
relation to the latter to provide therebetween data card space and
to provide between each input conductor and each readout conductor
a capacitive coupling that is subject to blocking by an intervening
conductive shield of a data card in said space, a plurality of
voltage stabilizing capacitors corresponding to said respective
readout conductors, each of said voltage stabilizing capacitors
having an input side and an output side, the output side of each
voltage stabilizing capacitor being connected t the corresponding
readout conductor, a plurality of voltage stabilizing amplifiers
corresponding to the respective readout conductors and being high
gain voltage amplifiers with high input impedance, each of said
voltage stabilizing amplifiers having its input connected to the
corresponding readout conductor and having its output connected to
the input side of the corresponding voltage stabilizing capacitor,
the voltage stabilizing amplifier and the voltage stabilizing
capacitor connected to each readout conductor having respectively a
gain and a capacitance mutually related to each other to effect in
response to an incipient change in voltage on the corresponding
readout conductor a restoration of the original voltage on the
readout conductor by a flow of electrical charge between the
capacitor and the readout conductor induced by an amplified change
in voltage applied by the amplifier to the input side of the
capacitor so that the voltage on the readout conductor remains
substantially unchanged by the energization of any of said input
conductors to which the readout conductor is capacitively coupled
through an aperture in the electrical shield interposed
therebetween, and information-receiving means coupled to said input
side of each of said voltage stabilizing capacitors to respond to
the change of voltage applied to said input side of the capacitor
by the corresponding voltage stabilizing amplifier as an incident
to energization of an input conductor to which the corresponding
readout conductor is coupled capacitively through an aperture in an
intervening electrical shield.
2. Apparatus for reading a data storage element incorporating an
electric shield apertured selectively in a pattern representing
recorded information, said apparatus comprising, in combination, a
plurality of input conductors for disposition along one side of a
data storage element to be read, means for energizing said input
conductors selectively, a plurality of readout conductors for
disposition along the opposite side of the data storage element to
be read to provide between individual input conductors and
individual readout conductors capacitive couplings that are subject
to blocking by a data storage element intervening between the input
conductors and the readout conductors and incorporating an electric
shield defining selectively positioned apertures providing for
unblocked capacitive coupling therethrough of individual input
conductors with individual readout conductors, a plurality of
voltage stabilizing capacitors corresponding to said respective
readout conductors, each of said voltage stabilizing capacitors
having an input side and an output side, the output side of each
voltage stabilizing capacitor being coupled to the corresponding
readout conductor, a plurality of voltage stabilizing amplifiers
corresponding to the respective readout conductors, each of said
voltage stabilizing amplifiers having its input coupled to the
corresponding readout conductor and having its output coupled to
the input side of the corresponding voltage stabilizing capacitor,
the voltage stabilizing amplifier and the voltage stabilizing
capacitor corresponding to each readout conductor having
respectively a gain and a capacitance mutually related to each
other to effect in response to an incipient change in voltage on
the corresponding readout conductor a substantial restoration of
the original voltage on the readout conductor by a flow of
electrical charge between the capacitor and the readout conductor
induced by a change in voltage applied by the amplifier to the
input side of the capacitor as an incident to the energization of
any of said input conductors to which the readout conductor is
capacitively coupled through an aperture in the electrical shield
disposed therebetween and information-receiving means coupled to
said input side of each of said voltage stabilizing capacitors to
respond to the change of voltage applied to said input side of the
capacitor by the corresponding voltage stabilizing amplifier as an
incident to energization of an input conductor to which the
corresponding readout conductor is coupled capacitively through an
aperture in an intervening electrical shield.
3. Apparatus for reading a data storage element incorporating an
electric shield apertured selectively in a pattern representing
recorded information, said apparatus comprising, in combination, a
plurality of energizable input conductors for disposition alongside
a data storage element to be read, a plurality of readout
conductors for disposition alongside the data storage element to
provide between the input conductors and the readout conductors
capacitive couplings that are subject to blocking by an intervening
data storage element incorporating an electric shield defining
selectively positioned apertures providing selectively for
unblocked capacitive coupling therethrough of individual input
conductors with individual readout conductors, a plurality of
voltage stabilizing capacitors having outputs coupled with said
respective readout conductors, a plurality of voltage stabilizing
amplifiers having inputs coupled with said respective readout
conductors and having outputs coupled to inputs of the
corresponding voltage stabilizing capacitors, the voltage
stabilizing amplifier and the voltage stabilizing capacitor
corresponding to each readout conductor having respectively a gain
and a capacitance mutually related to each other to effect as an
incident to the energization of any of said input conductors to
which the readout conductor is capacitively coupled through a
shield aperture a substantial restoration of the original voltage
on the readout conductor by a flow of electrical charge between the
capacitor and the readout conductor induced by a change in voltage
applied by the amplifier to the capacitor, and
information-receiving means coupled to respond to the change of
voltage applied to said respective voltage stabilizing capacitors
by the corresponding voltage stabilizing amplifiers as an incident
to energization of individual input conductors to which the readout
conductors are coupled capacitively through shield apertures.
Description
The present invention relates to apparatus for reading information
recorded in apertured data cards and more particularly to data card
reading apparatus which operates by capacitively sensing
information apertures in data cards incorporating thin electric or
electrostatic shields.
It has been recognized that the use of data cards incorporating
thin electric shields, which can be apertured selectively to record
information, offers many potential advantages. The electric shield
formed normally by a thin layer of electrically conductive material
incorporated into the card can be apertured selectively in various
positions to record information by punching the card, for example,
or in any preferred alternative manner as by photographic etching
or the like. Moreover, the fact that it is unnecessary to make more
than one direct electrical connection with each card minimizes the
likelihood of error arising from poor connections with the
cards.
A potentially advantageous approach to sensing the number and
positions of the apertures representing recorded information
involves the positioning of conductors of card reading apparatus
adjacent opposite sides of a card to be read and the sensing of a
shield aperture by active electrical capacitance established
between individual conductors on opposite sides of the card.
Heretofore, the potential advantages to be realized from the use of
data cards incorporating apertured electric shields and the
capacitive sensing of shield apertures representing recorded
information have not been fully realized, as a practical matter, on
account of inaccuracies and functional difficulties that have
heretofore constituted serious problems in the capacitive reading
of such cards with assured accuracy. More particularly, the
functional capabilities and accuracy of card reading apparatus
designed to capacitively sense information apertures in data cards
have been adversely effected by the presence and effect of spurious
and parasitic capacitive relationships to adjacent structure of the
conductors which sense the presence and location of individual
apertures.
In the operation of prior card reading apparatus, such spurious and
parasitic capacitance have been a source of errant signals and
"noise" that have interfered with reliable and accurate functioning
of the card reading apparatus.
One object of the invention is to provide for reading data cards
incorporating electrically conductive shields apertured to record
information, new and improved data card reading apparatus that
prevents spurious and parasitic capacitive relationships between
the card reading conductors from having an adverse effect on
accurate and reliable reading of the cards through the capacitive
sensing of the presence and location of shield apertures
representing recorded information.
Another object is to provide for the capacitive reading of data
cards of the character recited, new and improved card reading
apparatus that deals in most effective and practical manner with
problems of noise and spurious signals previously associated with
the capacitive reading of such cards to provide to associated
information receiving means accurate and reliable reading of
information recorded in the cards.
A further object is to provide data card reading apparatus of the
character recited which functions to maintain readout conductors,
which capacitively sense the presence and location to capacitively
apertures, at a substantially constant voltage level to prevent the
input to associated information receiving means from being
adversely effected as a practical matter by noise and spurious
signals arising from parasitic capacitive relationships of the
readout conductors to adjacent structure.
A further and more specific object is to provide data card reading
apparatus of the character recited in which the voltage of
individual readout conductors which function to capacitively sense
the presence and location of individual apertures is stabilized by
the flow of electrical charge between the individual readout
conductors and voltage stabilizing capacitors connected with the
respective readout conductors and having input sides connected with
the outputs of voltage stabilizing amplifiers corresponding to the
respective readout conductors and having inputs connected with the
respective readout conductors, the capacitance of the voltage
stabilizing capacitor and the gain of each voltage stabilizing
amplifier coacting with each readout conductor being coordinated in
design to operate in response to an incipient change in voltage on
the readout conductor, incident to charging of an input conductor
to which the readout conductor is capacitively coupled through a
card aperture, to restore continuously the original voltage on the
readout conductor so that the input to information receiving means
is not rendered inaccurate by spurious signals or noise arising
from spurious and parasitic capacitive relationships of the readout
conductors to adjacent structure, the information receiving means
being connected to the sides of the respective voltage stabilizing
capacitors opposite from the readout conductors.
Other objects and advantages will become apparent from the
following description of the exemplary embodiment of the invention
illustrated in the drawings, in which:
FIG. 1 is a simplified plan view of data card reading apparatus
incorporating the invention, certain parts being broken away to
reveal underlying structure and other components being illustrated
schematically and diagrammatically;
FIG. 2 is a fragmentary sectional view on an enlarged scale taken
along the line 2-2 of FIG. 1;
FIG. 3 is a fragmentary perspective view of the apparatus of FIG. 1
in which dielectric components of the data card and reading
apparatus are eliminated for clearness in illustration and
significant capacitive relationships are illustrated symbolically
with phantom lines used in the symbolic illustration of parasitic
capacitances; and
FIG. 4 is a diagrammatic view on a much enlarged scale of
electrical circuitry used in obtaining reliable and accurate
capacitive sensing of the presence and location of apertures
representing recorded information.
In a general way, the data card reading apparatus embodying
applicant's invention and denoted generally by the number 10 in
FIGS. 1 and 3 comprises a grid 12, FIG. 3, of individually separate
card-reading conductors 14, 16 having a capacitive relationship to
each other.
The conductors 14 are a series of spaced, parallel input conductors
adapted to be disposed adjacent one side of a data card 18 to be
read. The conductors 16 constitute a series of spaced, parallel
output or readout conductors oriented in transverse crossed
relation to the input conductors 14, as illustrated in FIGS. 1, 2
and 3, and being adapted for disposition adjacent the opposite side
of a typical data card 18 to be read. As will appear, the input
conductors 14 and the readout conductors 16 are spaced from each
other sufficiently to accommodate therebetween a card 18 to be read
and such layers of dielectric material as may be necessary or
desirable for insulating purposes while at the same time providing
between each input conductor 14 and each readout conductor 16 a
capacitive coupling subject to selective blocking by an intervening
data card 18 as will presently appear.
The typical data card 18 to be read comprises a thin layer of
electrically conductive material 20 which functions, when the card
is interposed between the input conductors 14 and the readout
conductors 16 for card reading purposes, to generally block the
capacitive coupling of the individual input conductors 14 to the
individual readout conductors 16 except where capacitive coupling
of individual input conductors 14 with individual readout
conductors 16 is specifically provided selectively by apertures
formed in the electric shield 20 in positions aligned with mutually
confronting portions of the input and readout conductors that are
to be selectively coupled capacitively. In the drawings, typical
apertures in the thin layer of conductive material 20 which, for
convenience, will be referred to as an "electric shield" or
"electrostatic shield" are denoted by the number 22.
As is well understood in the art of recording and retrieving
information by means of data cards of this character, the number
and positions of the apertures 22 formed in the shield 20 represent
information recorded in code and sensed in the manner to be
described.
The present invention contemplates that the apertures 22 will be
formed selectively in the shield 20 in any preferred manner such,
for example, as by punching, photographic etching or other process
that may be deemed most advantageous.
In the construction illustrated, the thin electrically conductive
shield 20 of the card 18 is laminated onto a dielectric base layer
24 of the card, which may be formed of paper. The apertures 22 may
or may not extend through the base layer 24, depending upon the
manner in which the apertures are produced in the shield 20.
For the purpose of illustration, the card 18 is oriented so that
the base layer 24 confronts the readout conductors 16 and forms an
electrical insulator between the readout conductors 16 and the
electric or electrostatic shield 20. To insulate the input
conductors 14 from the card shield 20, a layer 26, FIGS. 1 and 2,
of dielectric material is incorporated into the reading apparatus
10 to intervene between the series of input conductors 14 and the
conductive card shield 20, the dielectric insulating layer 26 being
limited in thickness to enhance the capacitive relationship
provided between the input conductors and the readout conductors by
virtue of their physical proximity to each other as disposed on
opposite sides of the thin shield 20 electrically perforated by
apertures representing encoded information. The electrical
capacitance established between each input conductor 14 and each
readout conductor 16 by reason of the positional relationship of
the input conductors and readout conductors to each other and
operating through individual apertures 22 in the shield 20 to
capacitively couple individual in conductors 14 to individual
readout conductors 16 is represented in FIG. 3 by symbols for
electrical capacitance shown in solid lines and denoted by the
number 28.
As previously indicated, the electrical capacitance 28 normally
coupling individual input conductors 14 with individual readout
conductors 16 is blocked by the intervening electric shield 20 of
the card 18 being read except where an aperture 22 appears in the
shield 20 in alignment with mutually crossing portions of an
individual input conductor and an individual readout conductor. The
electric shield 20 of the card 18 being read is preferably
grounded, as indicated diagrammatically in FIGS. 1 and 3, by
contact of the shield with a grounded contact 30.
With reference to the construction illustrated, the locations in
which the shield 20 can be apertured to record information are
disposed in longitudinal rows which align with the respective
readout conductors 16 nd transverse columns which align with the
respective input conductors 14, as indicated in part by the
apertures 22 appearing in FIG. 1.
To read a typical card 18, the input conductors 14 are briefly
energized sequentially in any desired order that may be programmed
into the card reading machine 10 using generally conventional input
conductor energizing means illustrated schematically in FIGS. 1 and
3 and denoted by the reference number 32. Normally, energization of
an input conductor 14 consists in applying a voltage to the
conductor so that its voltage is temporarily changed from the
normal voltage of the input conductors. The presence and position
of any information recording apertures 22 formed in the shield 20
in alignment with the particular input conductor 14 energized is
sensed by the readout conductors 16. As previously explained, the
presence of an aperture 22 in the shield 20 in alignment with a
particular input conductor 14 that is energized and a particular
readout conductor 16 provides for coupling of the input conductor
and readout conductor mutually aligned with the aperture by the
coupling capacitance 28, FIGS. 2 and 3. Consequently, the change in
voltage of any particular input conductor 14 that is energized
tends to effect a change in voltage on each of the readout
conductors 16 that is capacitively coupled through a shield
aperture 22 with the energized input conductor 14.
The number of readout conductors 16 that may be subject to a change
in voltage as an incident to energization of any particular input
conductor 14 may vary to include all of the readout conductors 16,
none of the readout conductors 16 or any intermediate number of the
readout conductors depending upon the number of shield apertures 22
that are mutually aligned with the particular input conductor
energized and the individual readout conductors.
It would appear, therefore, to be a simple matter to sense the
changes in voltage on the individual readout conductors 16 effected
as a consequence of energization of a particular input conductor 14
and thereby determine the number and location of any data recorded
on apertures 22 aligned with the energized readout conductor.
However, this approach, which appears logical and effective, has
heretofore been attended by serious problems of a practical
character which have restricted and inhibited the commercial
adoption and usage of data cards including an electric shield and
designed for capacitive reading of apertures representing
information.
In this connection, it should be borne in mind that there are
practical limitations on the capacitance 28 that can be provided
through an aperture 22 to couple an individual input conductor to
an individual readout conductor, this limitation of coupling
capacitance being due to practical limitations on the size of the
apertures 22, which aperture-size limitations arise in turn from
the practical necessity for providing for a substantial number of
longitudinal rows and transverse columns of apertures on a data
card of a practical size.
On account of these practical considerations, the capacitance 28 by
which a readout conductor 16 is coupled through an aperture 22 with
an individual input conductor 14 is rather limited. At the same
time, each readout conductor 16 is capacitively coupled to each
adjacent readout conductor 16 and, in varying degrees, to all of
the readout conductors 16 by reason of the proximate parallel
relation to the readout conductors 16 to each other. The capacitive
coupling of each readout conductor 16 to each of the immediately
adjacent readout conductors 16 is represented symbolically in FIG.
3 by a symbolic representation of capacitance denoted by the number
34. A capacitive coupling of each readout conductor 16 to each of
the more remote readout conductors 16 exists significantly, but is
not represented graphically in FIG. 3 for the sake of clarity.
Also, each readout conductor 16 is capacitively coupled to the card
shield 20 to which all the readout conductors are coupled
capacitively. The capacitive coupling of each readout conductor 16
to the shield 20 as a whole arises from the proximity of the
conductor to the shield 20 and is represented graphically in FIG. 3
by a phantom symbolic representation of capacitance denoted by the
reference number 36.
Heretofore, information receiving means that has responded to
changes in voltage of readout conductors 16 as an expedient for
sensing the presence and location of apertures in cards of the
character described has been subject to deception and other
functional problems involving inaccuracies and unreliability
arising from spurious signals and "noise" generated as a
consequence of voltage increase in the various readout conductors
which are capacitively coupled not only to individual input
conductors 14 through the shield apertures 22 but also to other
readout conductors and adjacent structure that is subject to
indeterminate and varying changes in voltage.
As previously intimated, problems of this kind have, as a practical
matter, complicated and inhibited the use of capacitively read data
cards of the character referred to. Such operational problems,
previously complicating and interfering with proper functioning of
card reading apparatus of this character, are obviated in
applicant's apparatus in which the voltage on each readout
conductor 16 is stabilized continuously at its normal level, even
when the readout conductor is capacitively coupled through a shield
aperture 22 to an input conductor 14 that is energized. The desired
stabilization of the voltage of each readout conductor 16 at its
normal level is provided by a plurality of voltage stabilizing
units 40 corresponding to the respective readout conductors, FIGS.
1, 3 and 4. Each voltage stabilizing unit 40 comprises a voltage
stabilizing capacitor 42 having an output side 44 connected to the
corresponding readout conductor 16 and having an input side 46
connected to the output 48 of a voltage stabilizing amplifier
denoted generally by the number 50, FIG. 4, and being preferably a
high gain voltage amplifier of high input impedance. The input 52
of each amplifier 50 is connected to the corresponding readout
conductor 16 and consequently to the output side 44 of the
corresponding voltage stabilizing capacitor 42.
By way of example, the capacitance 28 by which a typical readout
conductor 16 is coupled through a shield aperture 22 with an input
conductor 14 may be of the order of 1.5.times.10.sup..sup.- 13
farads. The voltage compensating capacitor 42 connected to each
readout conductor is selected to have a capacitance correlated with
the conductor coupling capacitance 28 and preferably being only a
small multiple of the corresponding capacitance 28. With reference
to the example mentioned, each voltage compensating capacitor 42
may advantageously have a capacitance of the order of
5.times.10.sup..sup.-13 farads.
By way of illustration, the circuitry of an exemplary voltage
compensating amplifier 50 having a high input impedance and a high
voltage gain is illustrated diagrammatically in FIG. 4. As shown,
the input 52 from the associated readout conductor 16 to the
typical amplifier 50 is connected to the gate 54 of an N channel
junction field effect transistor 56 which may, for example, be a
MPF-105. The source 58 of the transistor 56 is connected to a
positive 3-volt power source 60. The drain 61 of the transistor 56
is connected to the base 62 of a second transistor 64, which can be
a 2N4125. The collector 66 of the transistor 64 is grounded and the
emitter 68 of the transistor 64 is connected to the emitter 70 of a
similar transistor 72 that can also be a 2N4125. The collector 74
of the transistor 72 is connected to the output 48 of the amplifier
50 which, as previously indicated, is connected to the input side
of the voltage compensating capacitor 42.
A positive 12-volt power source 76 is connected through a 6000-ohm
resistor 78 with the source 61 of the transistor 56 and the base 62
of the transistor 64. The positive 12-volt power source 76 is also
connected through a 2000-ohm resistor 80 with the emitters 68, 70
of the respective transistors 64, 72. A positive 6-volt power
source 82 is connected to the base 84 of the transistor 72 and a
negative 6-volt power source 86 is connected through a 4000-ohm
resistor 88 with the collector 74 of the transistor 72.
Each voltage stabilizing amplifier 50 is preferably stabilized by
means of a resistor 90 connected between the output 48 and input 52
of the amplifier 50 and having a rather high resistance which can,
for example, be 2.times..sup.7 ohms. However, the input impedance
of the typical voltage compensating amplifier 50 is much greater
than the impedance of the stabilizing resistor 90 with the
consequence that the static voltages on the input 52 and output 48
of the amplifier 50 are nearly the same. If desired, the voltage of
the power supply source 60 can be adjusted for each amplifier to
compensate for deviations from design values which may be inherent
in the particular junction field effect transistor 56 used in the
amplifier and thereby assure equalization of the static voltage on
the amplifier output 48 with that on the amplifier input 52.
However, in most cases it is not necessary to adjust the voltage of
the source 60 to equalize the input and output voltages of the
amplifier because only pulses of short duration are transmitted
through the amplifier, the voltage applied by the amplifier to the
input 46 of the corresponding voltage compensating capacitor 42
being sensed, as will be explained, through a coupling capacitor
92.
With reference to the example described, the voltage on a
particular input conductor 14 being energized by the input
conductor energizing means 32 may be changed 10 volts from the
normal voltage applied by the energizing means 32 to all the other
input conductors 14. For any readout conductor 16 coupled through a
shield aperture 22 to the particular input conductor 14, energized
by a voltage differential of 10 volts as described, the apparatus
will produce on the input side 46 of the corresponding voltage
compensating capacitor 42 a voltage change of 3 volts. These
operating characteristics are mentioned illustratively by way of
example.
At the same time the voltage applied to the input side 46 of the
voltage compensating capacitor 42 changes as a consequence of the
corresponding readout conductor 16 being coupled through an
aperture 22 to an energized input conductor 14 in the manner
described, the voltage compensating capacitor 42 under the
electrostatic pressure of the changed voltage applied to the input
46 of the capacitor 42 functions to continuously maintain
substantially the normal voltage on the corresponding readout
conductor 16. In this connection, it will be appreciated that the
corresponding voltage compensating amplifier 50 responds to an
incipient change in voltage on the readout conductor 16 to exert
sufficient electrostatic pressure through the coacting voltage
compensating capacitor 42 to produce the desired maintenance of the
readout conductor substantially at its normal voltage level, the
effective functional values of the voltage compensating amplifier
50 and voltage compensating capacitor 42 being selectively designed
as described for this purpose.
As a consequence of each readout conductor 16 being maintained
substantially at its normal voltage during the sensing of all
apertures 22 aligned with a particular input conductor 14, the
spurious and parasitic capacitances 34, 36 by which the readout
conductors are coupled to adjacent structures do not interfere with
reliable and accurate sensing of the apertures.
It is also noteworthy that the transit or delay time lapsing
between the application of an energizing voltage to an input
conductor 14 and the consequent change in voltage on the input 46
of each voltage compensating capacitor 42 connector with a readout
conductor 16 which senses a shield aperture 22 is very short in
relation to other relevant time periods to be mentioned, being of
the order of 20.times.10.sup..sup.- 9 seconds. After effecting
quickly the change in voltage on the input side 46 of the
corresponding capacitor 42 requisite to restoring substantially the
normal voltage of the active readout conductor 16, the output
voltage of the corresponding amplifier 50 will slowly decay due to
leakage through the stabilizing resistor 90. For the component
values mentioned by way of example, the duration of the decay will
be of the order of 10,000.times.10.sup..sup.- 9 seconds. However,
this decay is of no consequence as the period during which each
input conductor 14 is energized and the sensing of shield apertures
22 aligned with the individual input conductor 14 is completed may
be limited to a period ranging from 100.times.10.sup..sup.- 9
seconds to 1,000.times.10.sup..sup.- 9 seconds. In other words, the
reading operation is completed long before the voltage decay on the
input 46 of the voltage compensating capacitor 42 has become
significant.
Moreover, by virtue of the high input impedance capabilities of
junction field effect transistors, such as the transistors 56
incorporated into the individual amplifiers 50, the amplifier
stabilizing resistors 90 can have resistances much higher than the
resistance mentioned by way of example. As a consequence, it is
practical to energize the individual input conductors 14 for
individual periods of time lasting considerably longer than the
1,000.times.10.sup..sup.- 9 second period mentioned. The capability
of the apparatus to handle such longer periods of energization of
the input conductors 14 allows sufficient time for the switching
transients within the information matrix conductors 16 to die out
before the voltages applied by the voltage compensating amplifiers
50 to the individual voltage compensating capacitors 42 is sensed
to determine the number and location of the shield apertures
aligned with the energized input conductor 14.
The voltages selectively applied to the inputs 46 of the voltage
compensating capacitors 42 in the manner described and representing
shield apertures 22 aligned with an energized input conductor 14
are coupled to information receiving means 94 having the capacity
of usefully storing, transmitting, tabulating or processing in any
desired manner the information represented by the apertures 22. As
illustrated, the input sides 46 of the respective voltage
compensating capacitors 42 are coupled to the information receiving
means 94 through the individual coupling capacitors 92.
By virtue of the suppression and effective elimination of the
troublesome consequences which would otherwise be manifest from the
spurious and parasitic capacitive relationships referred to and
troublesome "noise" previously attending the operation of prior
apparatus of this character, applicant's apparatus makes feasible
reliable and accurate sensing of shield apertures 22 of minimized
size.
Minimization of the size of the individual shield apertures 22 is
made possible by a large reduction in the coupling capacitance 28
between an individual input conductor 14 and an individual readout
conductor 16 required to effect reliable and accurate operation of
applicant's reading apparatus. It will be appreciated that
reductions in the size of the shield apertures 22 requisite to
reliable and accurate sensing of the presence of the apertures in
accordance with applicant's invention makes feasible the placement
of a larger number of apertures in a card of any particular size or
conversely a reduction in the size of the card required to
accommodate any particular number of apertures. This advantage can
be readily capitalized on by recording more information on a card
of given size, using the larger number of apertures made possible,
or by reducing the size of the card required to store a given
amount of information, or both, as it may be desired to capitalize
on the basic advantage of holes of minimized size.
While applicant's apparatus has been described in relation to the
sensing of apertures in an electric shield forming a component of a
card, it will be appreciated that the invention is applicable to
the capacitive sensing of information representing apertures in an
electric shield that may not necessarily be a component of a
card.
The invention is claimed as follows:
* * * * *